Turbochargers for gasoline and diesel internal combustion engines are known devices used in the art for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
The amount by which the intake air is boosted or pressurized is controlled by regulating the amount of exhaust gas that is passed through the turbine housing by a wastegate and/or by selectively opening or closing an exhaust gas channel or passage to the turbine running through the turbine housing. Turbochargers that are constructed having such adjustable exhaust gas channel are referred to in industry as variable geometry turbines (VGTs). VGTs typically include a movable member that is positioned within a turbine housing between the exhaust gas source and the turbine. The movable member is activatable from outside of the turbine housing by suitable actuating mechanism to increase or decrease the volumetric flowrate of exhaust gas to the turbine as called for by the current engine operating conditions. Increasing or decreasing the volumetric flowrate of exhaust gas to the turbine respectively increases or decreases the intake air boost pressure generated by the compressor mounted on the opposite end of the turbine shaft.
U.S. Pat. No. 3,478,955 discloses a variable area diffuser for a compressor comprising a movable wall that is positioned within the compressor case and that is axially displaceable therein to move against an adjacent case wall. Moving the movable wall towards the adjacent case wall operates to decrease the volumetric flowrate of gas from the case discharge chamber to an impeller, thereby reducing the impeller's rotational speed. The movable wall is in the form of an annular ring that is disposed concentrically around the impeller and that is positioned within an annular groove in an axially facing surface of the case. Axial displacement of the movable wall within the case is controlled by a complex arrangement of posts that extend through the case, that are attached at one end to the movable wall, and that are attached at an opposite end to an actuating mechanism. The actuating mechanism includes a rotary control ring that is adapted to cause axial movement of the posts and attach movable wall by rotary control ring movement around the compressor case.
A concern of such design is the use of a complex actuating mechanism that could be prone to operating problems or failure. An additional concern is the need to use numerous sealing components to prevent the passage of exhaust gas through the case between the moveable wall and actuating posts.
U.S. Pat. No. 4,886,416 discloses an exhaust gas turbocharger comprising a sliding sleeve positioned within a turbine housing between the exhaust gas source and the turbine. The sliding sleeve is adapted to both rotate and move axially within the turbine housing to increase or decrease the volumetric flowrate of exhaust gas to the turbine. The sliding sleeve is operated by a driving ring that is rotatably mounted within the housing adjacent the sliding sleeve, and that is put into rotational operation by gear interaction with a rotary actuating lever. The sliding sleeve includes a axial slot and a helical slot in its surface that cooperates with a respective driving pin (projecting, from the rotatable driving ring) and a slot pin (projecting from the fixed housing). The sliding sleeve is both rotated and moved axially within the turbine housing by rotation of the driving ring, which in turn causes the driving pin to engage the sliding sleeve axial slot and effect axial/rotational movement via engagement of the sliding sleeve helical slot and slot pin.
In an effort to simplify the operation of VGTs, and optimize efficient operation of the same, it is desired that a VGT be constructed having an exhaust gas flow path adjustment mechanism configured to provide such adjustment in a simple manner within a turbine housing. Is it desired that the adjustment mechanism be configured to permit actuation using a simplified actuating mechanism having minimum number of moving parts.